1. Field of the Invention
This invention relates to a binder used in shaping articles from particulate materials for manufacturing high precision, high density and high integrity engineering parts from particulate materials, such as metal powders or particles, ceramic powders of particles of the like by injection molding or similar processes, and the method of formulating the binder.
2. Art Background
Injection molding processes have increasingly been used to form articles from particulate materials. This process enables the formation of small parts with more complex geometry at even lower cost than conventional forming processes.
Classically, particulate materials are mixed with a binder and then injection molded into a desired configuration which is generally called a green body. The binder contained in the green body is removed by thermal degradation prior to sintering. The body is sintered to obtain the desired part with 90-96% density of the theoretical.
The binder plays a key role in the injection molding process. As a carrier, it facilitates flow and packing of the particulate materials into the mold cavity and holds the particles in the shape of the mold after the part is ejected. When the green body is successfully formed, the binder finishes its function as a carrier and needs to be removed from the green body prior to sintering. The removal of the binder is performed by means of thermal heating, or solvent washing, or combinations thereof. This removal has to be fast, without creating any defects in the green body configuration or leaving behind any residues which hinder densification of the body during sintering.
The selection of a binder is generally based on its flow characteristics. The slow binder removal process required in this process remains the major drawback of the process despite the disclosure of various binders in the art. Much effort has been directed towards reducing the debinding time through change of debinding techniques. This invention permits a reduction in debinding time of thermal degradation through the formulation of binder systems which are not disclosed in the prior art.